The present invention relates generally to heat and mass transfer columns and, more particularly, to liquid flow distributors used in such columns and methods of distributing liquid using such flow distributors.
Mass transfer columns are configured to contact two fluid streams of differing characteristics with one another in order to effect mass and/or heat exchange between the different phases. The term “mass transfer column” as used herein is not intended to be limited to columns in which mass transfer is the primary objective of the processing of the fluid streams within the column, but is also intended to encompass columns in which heat transfer rather than mass transfer is the primary objective of the processing. Some mass transfer columns, such as those utilized in multicomponent distillation and absorption applications, contact a gas or vapor stream with a liquid stream, while others, such as extraction columns, may be designed to facilitate contact between two liquid phases of different densities. Oftentimes, mass transfer columns are configured to contact an ascending vapor or liquid stream with a descending liquid stream, usually along multiple mass transfer surfaces disposed within the column. Commonly, these transfer surfaces are defined within one or more regions or beds of random or structured packing material configured to facilitate intimate contact between the two fluid phases. As a result, the rate and/or degree of mass and heat transferred between the two phases in enhanced.
In order to ensure maximum contact between the two fluid phases in a mass transfer column, the descending liquid phase must be uniformly distributed as it enters a packing bed from an overlying region of the column. Uneven distribution reduces contact between the two phases and disrupts the liquid/vapor or liquid/liquid ratio along the cross-section of the column, which should be maintained substantially constant during proper operation of the column. Various types of liquid distributors have been designed with the objective of uniformly dispersing liquid across the upper surface of a packing bed, while still providing low pressure drop, minimal fouling, and a wide performance window.
Most distributors deliver liquid onto the surface of the packing at a number of spaced-apart locations, referred to as drip points. In fact, the drip point density is a measure of the distribution performance of a particular distributor. Additionally, the size of the droplets formed at the drip points is also important. If the droplets are too large, the drip points, too, may also be too large and the horizontal distribution of the liquid across the surface of the packing may be hindered. If the droplets are too small, the liquid risks being entrained in the ascending vapor or gas and carried out of the column thereby reducing the efficiency of the heat and/or mass transfer within the column.
Thus, a need exists for a liquid distributor that has the capability of providing more uniform distribution of liquid per unit of packed bed surface along a series of spaced, flow drip points. The distributor should still exhibit desirable operating characteristics, such as low pressure drop, resistance to fouling, and performance at low turn down, while being robust and flexible enough to be utilized in a wide variety of heat and mass transfer operations.